The present invention relates to a waste water treatment method and plant, more particularly to a waste water treatment method and plant designed for biological treatment of the organic and inorganic substances in the waste water for obtaining purified water by using granular carriers formed mainly from a macromolecular substance or an inorganic substance capable of carrying microorganism having water-purifying ability in a inclusively-immobilized form or adhesively-immobilized form or bindingly-immobilized form.
As generally known, the existing waste water treatment plant is available in the forms of the standard activated sludge process reaction tank, immobilized microorganism carrier reaction tank and the like. The immobilized microorganism carrier reaction tank is advantageous over the standard activated sludge process reaction tank in that the microorganism concentration can be maintained at a higher level for decomposing the organic and inorganic substances in the waste water with a higher efficiency. The reaction tank provided with air blower is called an aeration tank.
FIG. 10 is a schematic diagram showing a waste water treatment plant designed for using immobilized microorganism carriers, wherein A is a plan view and B, a cross-sectional view along X-Y line of the plan view. The waste water treatment plant shown in the diagram B of the same figure is a plant comprising an overall air blowing type aeration tank, that is, an aeration tank 1, about 5 m deep, containing immobilized microorganism carriers 2, an air blower 3, for blowing the air covering all over the bottom of the tank, and an air blowing pipe 3a connected to the air blower 3. Normally, the overall air blowing type air blower 3 is installed 200 mm to 600 mm above the bottom of the tank. With this air blower 3, the speed of water flow created by the blow of air from the bottom of the tank is not high enough for producing a stirring effect sufficient for liquidizing the carriers 2, thereby making the carriers 2 tend to precipitate on the bottom of the tank as precipitate 9. The numeral 8 represents the inlet of the waste water to be treated.
The waste water treatment plant shown in FIG. 10 has a shortcoming that the precipitation of the carriers under the air blower 3 causes the formation of a dead space in the aeration tank 1 and the resulting shortage of the carriers necessary for the treatment, which results in the decline of the water treatment capacity of the water treatment plant. In order to prevent the carriers from precipitating under the air blower 3, conventionally employed method has been such as filling the space under the air blower 3 with urethane resin or the like or supplying additional carriers for covering its shortage, thereby preventing the decline of the treatment capacity of the plant.
The method of filling the space under the air blower 3 with the urethane resin or the like, as being a means for preventing the carriers 2 from precipitating under the blower 3, has a shortcoming that this incurs the additional material cost and labor cost for the refill of the urethane resin. Further, since the space under the air blower filled with the urethane resin or the like becomes a dead space, this gives rise to a problem, that is, in order for the reaction tank to maintain a necessary cubic volume, it is necessary for the reaction tank to have a design cubic volume including the dead space, which results in the increase in the construction cost.
Further, such a waste water treatment plant is required to prevent the decline of its treatment capacity by supplying additional carriers corresponding to the carriers precipitated under the air blower 3, and the plant designed in this way gives rise to a problem such as the increase in the cost of carriers as the quantity of the necessary carriers increases. Furthermore, such conventional plant has shortcomings such as the decrease in actually available cubic volume of the reaction tank due to the formation of the dead space under the air blower by being occupied by the precipitate of the carriers, which results in poor treatment effect and resulting poor quality of treated water due to the decomposition of the sludge formed among the spaces of the precipitated carriers.
Thus, the object of the present invention is to resolve the problems as are described above by providing a waste water treatment method and plant capable of preventing the immobilized microorganism carriers from precipitating under the air blower installed with the reaction tank or the aeration tank.
The first aspect of the invention relates to a waste water treatment method by using an aeration tank containing the carriers capable of growing microorganism for biological treatment of waste water or a subunit of the aeration tank joined with the aeration tank through a partition wall including the screen capable of separating the carriers, an oxygen-supplying air blower for the subunit of the aeration tank and an air bubble generator installed under the air blower, wherein the air bubbles from the air bubble generator is used for creating the flow of the water for liquidizing the carriers under the air blower, thereby preventing the carriers from precipitating under the air blower.
More specifically, the invention relates to a waste water treatment plant comprising an aeration tank containing the carriers for growing the microorganism for biological treatment of waste water or the subunit of the aeration tank joined with the aeration tank through a partition wall including the screen capable of separating the carriers, oxygen-supplying air blower for the aeration tank or the subunit of the aeration tank and submerged stirrer for generating air bubbles to create the flow of water for liquidizing the carriers under the air blower. According to this arrangement, the air bubbles from the air bubble generator creates the water flow to liquidize the carriers under the air blower and remove the carriers on the bottom of the aeration tank under the air blower, thereby maintaining the treatment efficiency required for the aeration tank or reaction tank and the designed treatment performance.
Further, the invention relates to a water treatment plant comprising a plurality of air bubble generators installed under the air blower and arranged in parallel or orthogonally to the direction of the flow of the waste water or along one or both of the side walls of the aeration tank, wherein the precipitation of the carriers can be prevented effectively by generating the air bubbles by the air bubble generators in those places where the carriers are apt to precipitate.
Still further, the invention relates to a waste water treatment plant comprising the air bubble generators installed at equal intervals between any of opposing pairs of the side walls of the aeration tank or the subunit of the aeration tank, wherein the air bubble generators are installed at those places where the carriers are apt to precipitate, thereby enabling the air bubbles to be generated to effectively create the flow of the water that prevents the precipitation of the carriers.
Yet further, the invention relates to a waste water treatment plant comprising the air bubble generators installed at equal intervals of 2 m to 20 m between any of opposing pairs of the side walls of the aeration tank or the subunits of the aeration tank, wherein the flow of the water can be created throughout the space under the air blower and the carriers can easily be set afloat. Further, it is preferable for the air bubble generators to be installed at equal intervals of 2 m to 10 m.
Still further, the invention relates to a waste water treatment plant comprising the air bubble generators provided with an air bubble outlets for discharging the air bubbles towards the bottom of the aeration tank, wherein the suspendibly afloat carriers which tend to precipitate on the bottom of the tank is set afloat by the air bubbles blown towards the bottom of the tank, thereby enabling the carriers to be effectively utilized for the growth of the microorganism which is capable of decomposing the organic macromolecular substance and the like in the waste water.
The second aspect of the invention relates to a waste water treatment method by using an aeration tank containing the carriers of growing microorganism for biological treatment of the waste water or the subunit of the aeration tank joined with the aeration tank through a partition wall including the screen capable of separating the carriers and oxygen-supplying air blower for the aeration tank or the subunit of the aeration tank, wherein submerged stirrer installed under the air blower creating the flow of water to liquidize the carriers for preventing the carriers from precipitating under the air blower.
Further, the invention relates to a waste water treatment plant comprising an aeration tank containing the carriers for growing microorganism for biological treatment of waste water or the subunit of the aeration tank joined with the aeration tank through a partition wall including the screen capable of separating the carriers, oxygen-supplying air blower for the aeration tank or the subunit of the aeration tank and submerged stirrer installed under the air blower. This arrangement provides a plant wherein the carriers under the air blower is liquidized by the flow of the water created by the submerged stirrer to prevent the carriers from precipitating under the air blower, whereby the reaction tank can be kept capable of operating with designed efficiency and designed treatment performance without forming any dead space.
Still further, the invention relates to a waste water treatment plant comprising the submerged stirrers installed at intervals of 2 m to 20 m on the bottom of the tank, wherein the flow of the water can be created throughout the space under the air blower to set all the carriers suspendibly afloat and distributed throughout the tank, thereby enabling the plant to maintain its designed capacity for decomposing the organic macromolecular substance in the waste water.
The third aspect of the invention relates to a waste water treatment method by using an aeration tank containing carriers for growing microorganism for biological treatment of waste water or the subunit of the aeration tank joined with the aeration tank through a partition wall including the screens capable of separating the carriers, oxygen-supplying air blower for the aeration tank or the subunit of the aeration tank and a supply pipe for supplying the water to be treated into the tank for creating the flow of water or circulation of water under the air blower to prevent the precipitation of the carriers under the air blower, wherein the supply pipe is installed under the air blower so that the water to be treated flowing along the bottom of the tank creates the flow of water to liquidize the carriers on the bottom of tank to prevent the precipitation of the carriers.
Further, the invention relates to a waste water treatment method characterized by that the direction of the water to flow on the bottom of the tank or the direction of the circulating water is reverse to the direction of the flow of the treated water, wherein the flow of water to be treated along the bottom of the tank is made reverse to the direction of the flow of treated water to create the circulating flow of water to set the carrier suspendibly afloat for enabling the carriers not only to be kept in contact with the water to be treated for a sufficient length of time but also to be prevented from precipitating, thereby reducing the number of the carriers which are unable to contribute to the biological treatment of the waste water.
Still further, the invention relates to a waste water treatment plant comprising an aeration tank containing the carriers for growing microorganism for biological treatment of waste water or the subunit of the aeration tank joined with the aeration tank through a partition wall including the screen capable of separating the carriers, oxygen-supplying air blower installed under the aeration tank or the subunit of the aeration tank, water supply pipe having a number of outlets for letting the water to be treated flow into the tank and installed under the air blower so as to create the flow of the water reverse to the flow of the treated water, wherein the water supply pipe is installed in the direction of the width of the aeration tank so that the water to be treated discharged from the outlets creates the flow of water or circulation of water reverse in direction to the direction of the flow of the treated water on the bottom of the tank, thereby preventing the precipitation of the carriers.
Yet further, the invention relates to a waste water treatment plant characterized by that the supply pipes are arranged orthogonal to the direction of the flow of the treated water and at intervals of 2 m to 20 m along the direction of the flow of (water) on the bottom of the tank, wherein the flow of the water can be created covering all over the bottom of the tank depending on the size of the tank, thereby preventing the precipitation of the carriers.